A252732 In view of their definitions, let us refer to A251964 as sequence "5", A252280 as sequence "7", and similarly define sequence "prime(n)"; a(n) is the third term of the intersection of sequences "5", ..., "prime(n)".
7, 7, 7, 7, 421, 2311, 43321, 59730109, 537052693
Offset: 3
Programs
-
Mathematica
s[p_, k_] := Module[{s = Total[IntegerDigits[p^k]]}, s/2^IntegerExponent[s, 2]]; f[p_,q_] := Module[{k = 1}, While[ ! Divisible[s[p, k], q], k++]; k]; okQ[p_,q_] := s[p, f[p,q]] == q; okpQ[p_,nbseq_] := Module[{ans=True}, Do[If[!okQ[p,Prime[k+2]], ans=False; Break[]],{k,1,nbseq}]; ans]; a[n_]:=Module[{c=0, p=2},While[c<3 , If[okpQ[p,n],c++];p=NextPrime[p]];NextPrime[p,-1]]; Array[a,6] (* Amiram Eldar, Dec 09 2018 *) -
PARI
s(p, k) = my(s=sumdigits(p^k)); s >> valuation(s, 2); f(p, vp) = my(k=1); while(s(p,k) % vp, k++); k; isok(p, vp) = s(p, f(p, vp)) == vp; isokp(p, nbseq) = {for (k=1, nbseq, if (! isok(p, prime(k+2)), return (0));); return (1);} a(n) = {my(nbpok = 0); forprime(p=2, oo, if (isokp(p, n), nbpok ++); if (nbpok == 3, return (p)););} \\ Michel Marcus, Dec 09 2018
Extensions
More terms from Peter J. C. Moses, Dec 21 2014
a(10)-a(11) from Michel Marcus, Dec 09 2018
Comments